Officer Manuel Ramos and Corporal Jay Cicinelli returned to court Tuesday for the second day of a preliminary hearing meant to determine if there is enough evidence to try the two men for the beating death of Kelly Thomas.

A judge listened as defense attorneys argued that Thomas did not die as a result of his altercation with police last summer, but rather a lack of oxygen caused either by compression from CPR or a delay of getting a breathing tube into Thomas.

Trauma surgeon Dr. Michael Lekawa, a medical examiner and the chief of trauma surgery at UCI Medical Center, where Thomas was taken after the altercation, took the stand Tuesday and described the consequences of hypoxia, a lack of oxygen in the blood. Lekawa said continuous compression of Thomas's chest during the confrontation caused breathing problems that led to his death. Hypoxia was the main cause of death given by the coroner.

"Did you determine a point during the altercation where you believed that there was chest compression sufficient to cause hypoxia?" John Barnett, defense attorney for Ramos, asked Lekawa.

"That's not an instantaneous moment. Hypoxia develops over time," said Lekawa.

Thomas, a homeless man with schizophrenia, was stopped the night of July 5, 2011, for allegedly trying to break into cars at the bus depot at the Fullerton Transportation Center. Officers stopped Thomas, 37, and asked him to sit on a curb, but he allegedly did not comply.

Prosecutors allege that's when Ramos punched Thomas in the ribs and tackled him to the ground, and minutes later Cicinelli Tasered him several times and struck him in the face eight times with the Taser. Thomas eventually lost consciousness and was treated at the scene by paramedics before being hospitalized. Thomas died five days later in a hospital after being taken off life support.

Ramos has pleaded not guilty to second-degree murder and involuntary manslaughter charges. Cicinelli has pleaded not guilty to involuntary manslaughter and excessive force under color of authority.

New video released Monday of the beating was shown again Tuesday. It shows Ramos and another officer swinging at Thomas with batons before they pin him to the ground. Cicinelli joined the altercation minutes later.

The 33-minute tape was paired with audio devices worn by some of the six officers who responded that night. Only Ramos and Cicinelli have been charged. All six officers were placed on administrative leave and face an internal investigation.

Ramos's defense attorney says there is not enough evidence for the case to go forward and that Ramos was only doing what he is "required and permitted to do."

A separate federal investigation is pending to see if Thomas's civil rights were violated.